central meridian

Quick Reference

An imaginary straight line joining the north and south poles of a planet's disk as seen from Earth. It is used as a reference for observers making longitude measurements of features on a planet. As the planet rotates, the time when a feature crosses, or transits, the central meridian is noted; its longitude can then be derived from published tables. Such observations are known as central meridian transit timings.

Subjects: Astronomy and Astrophysics.

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